Process for treating brightened electrotinplate



April 4, 1950 A. F. PRUST PROCESS FOR TREATING BRIGHTENED ELECTROTINPLATE Filed Dec. 15, 1944 INVENTOR. A L V/N FEEDER/CK P/PUST Patented Apr. 4, 1950 PROCESS FORTREATINGBRIGHTENED ELECTROTINPLATE/ Alvin 1 Frederick Pru st Warren, Ohio; assignor, to-

Republic. Steel Oorporation,-,. Cleveland, Ohio, a. corporation of New J e'rscy Application'December l5, 194.43.,SerialiNo;- 5683415 5 Claims. (01. 2049-141) 1 This invention relates generally; to the tin,- plate artandparticularlyto a new and-improved? method-of and apparatus for treating, the surfaces of electro-tinplate.

Electro-tinplate, that is; steel having surface;

coatingsofelectro-deposited tin; asmade heretofore; does-not adhere strongly or uniformly to enamel or lacquer. Whensuch surfaces have,- been brightened; .asby beingfused after electrodeposition of the tin. they often becomediscolored with a yellow discoloration, and there is a-tendency for lacqueror enamelwhieh has been baked thereon to loosen fromthe tin or actually. to fiake ofi. I- believe that when electro-tinplate is brightenedthesurface-layers of the tin are; activated and oxidized; and that when-such. 3."; surface is-enameled or lacquered; at tempera tures-which may range up to about 420 F., the oxide on or: the oxidationof the tin surface layer forms a weak connectionbetween the enamel, or lacquer andthe tin-whichis. not strong'enoughi toprevent the coating-material from loosening or flaking off;

The present invention aims to avoid those; causes of pooradherence and provides-amethodof and-apparatus for treatment of: brightened;- electro-tinplate so that enamel or lacquer will adhere tenaciously-due,. I-believe-,; to thepassive or: non-oxidized condition of the. surface layers; of the tin.

Briefly. stated, the present inventioncomprises, a treatment of brightened e-lectro-tinplate which; converts the surfacelayer of the: tin intea -de-- oxidized and passive state, that is, deoxidizes it:- and makes it resistant to oxidation, and protects it against-- oxidation as evidenced by discoloration, even when heated to a lacquering.tempera-- ture of about 420 F; This method of treatment comprises the steps of making a brightenedelectro-tinplate article the cathode in-a. heated: electrolyte containing hexavalent chromium and passing a low density current thru the electrolyte, surrounding, the article with a non-oxidizing atmosphere while washing'andlarg ely dryingcin; flash heating. it to complete drying; and 1711511. coating it with a protective coating;

An illustrative, but not-limitingsetof(2011;:

ditions under which" the. present invention has been satisfactorily practiced is as: follows:- A

piece of electro-tin-plate; with brightened surtime of treatment.

2, about .75%--byweight-of potassium chromate; current of between about 10 and about 15, amper-es persq; f t. and at avoltage of; about-7.5 volts-was passed thru; the electrolyte andv pieceof tinplate'; for about; one: second. The strip was then; washed; largely dried; in a steamatmosphere, finally and rapidly dried, andimmediately; coated with oil. Theelectrotinplate so heated did not? exhibit: any: tendency: to develop ayellow coloration when heated? at about 420- F; for

about twenty; minutes and enamel and lacquer baked on the: thus treated tinplate adheredtenaciously and; uniformly: to the tinplate and; exhibitedano tendency to: flake ofi;

ltvwillibevunderstood that the specific, condi-. tions set; out: inthe-foregoing= example maybe m'cdiiied considerably and. within:the-following? limits:

The temperature ofthe-- electroly-t e may: range betweeneabout 150 F: and; about 200 F. Temperatures lower than about 150 F. may be used; butiare non-desirable. In general, temperatures much. below aboutF18Q9-F. are notdesired because: the"- current requirements increase in inverse proportionsto. the decrease in temperature.

The length of' time the current is flowingthru any part of the article may range: from about one-half second" to about ten seconds. This range of timeis apparently determinedby the time required 1 for the-electrolyte to change sufficiently to attack'the tin'; It appears that the nature-'ofthe diffusion layer or cathode film is' a -function ofthe applied current density and: With a, constant current density;- the pH" value or alkalinity of the dif fusion layer rises in proportion to the time of treatment until its alkalinity becomes high enough to attack the tin. With. current densities within therange later specified herein, a treat'-. menttimiei'off as mllQhjasI about, ten seconds is; not" sufficiently 1 11'gf12f()v causeany bad effects on the; tin'platefresultingjfrom an attack of the tinbytheielectrolyte;

Current 'deiris'ities,v may be used which range from about; e c about 25 amp s p r sq ft! th the-best r sults being obta ned wit n th 'r neeiof from abcut 1.0; to 18,"amperes;'pr sq. ft.

Since the-voltage is a'f unctioneof the required; current den ity and'the-concentrationand tem-a perature oi the electrolyte. the; ranges; oi -voltages; are-fairly well deiined by those factors: Howe. ever, general-i it ay e a d: ha for t e.- rans a-ofr current densi yand-ccncen r tion d temperature of he soluti nssset out-here n ing on the voltage employed, the manner of rinsing the treated tinplate and the speed of travel of the tinplate thru the electrolyte. The limits just stated have been found to be satisfactory with tinplate traveling thru the electrolyte at the rate of about 100 to about 800 ft. per minute, with ordinary rinsing practice and with the voltages maintained within the foregoing limits.

The present process has been carried out successfully on a commercial scale under the following set of conditions: Electro-tinplate in endless strip form was passed at a speed of 250 ft. per minute, thru an electrolyte containing about .'75% of potassium chromate by weight while a current of about 4.5 volts and an amperage of about 10 to 18 amperes per sq. ft. was flowing thru the electrolyte and tinplate. The temperature of the electrolyte was about 180 F. The strip moved from the electrolyte thru a steam atmosphere into and out of a body of wash water and between steam jets which removed practically all the wash water and electrolyte from its surfaces. Then it was heated for a fraction of a second and thereby made substantially dry and immediately thereafter it was coated with an oil emulsion and heated to dry out that coat- The present invention will be better understood by those skilled in the art from the following description of the construction and operation of the apparatus illustrated in the drawing which is attached to and forms a part of this specification.

In the figure tinplate in the form of an elongated strip l passes from roll stand 2 between roll 3 and cathode roll 4 which constitutes part of an electric circuit. From roll 3 strip I moves vertically down between anodes 5, also in the electric circuit, and around roll 6 and thence upwardly to roll 1. The anodes 5 and roll 6 are positioned in a cell 8 which is substantially full of electrolyte. The strip l passes from roll 1 down to and around roll 9 and thence up to roll 10. Roll 9 is located near the bottom of cell H which is partly filled with condensed steam containing more or less electrolyte. The temperature of the electrolyte is controlled by heating coils I2 in the upper portion of cell 8 and the temperature of the liquid in cell II is controlled by heating coils [3 near the bottom of that cell. A hood l4 encloses the upper end of cell H and part of cell 8, and serves to retain a steam atmosphere around the strip in both cells abovethe surface of liquids therein. Just below roll in pipes l5 are disposed on opposite sides of the strip I and are provided with openings thru which steam may be discharged against the surfaces of the strip at an acute angle and in a direction opposite to the direction of travel of the strip as it moves from roll 9 to roll ID.

- Immediately after leaving roll l0, strip l passes between flash heater tubes 16 which extend along the strip for a distance of a little less than two feet. Then the trip passes into a spray chamber H where an oil emulsion is sprayed onto the surfaces of the strip thru perforations in tubes [8. Excess oil emulsion collects in tank 19 below this spray chamber l1 and may be repumped thru pipes [8. When the strip l leaves chamber I! it passes under roll 20 which dips into water in rinse tank 2| therebeneath and then passes upwardly between inclined heating tubes 22.

It will be understood that the flow brightened, oxidized, tinplate surfaces are deoxidized in passing between anodes 5 in the electrolyte in cell 8; that the strip is then protected against contact with the air while passing from the electrolyte into and out of the liquid in cell II; that the electrolyte is washed from the strip by the liquid in cell Ii and most of the moisture is removed from the strip by the jets of steam from steam pipes l5; that the remaining moisture on the strip is driven off by fiash heating, that is, by being heated for not more than about one second by the heater pipes [6; that immediately thereafter the surfaces of the strip are coated with a water-oil emulsion and the emulsion is spread more or less uniformly over the surfaces by the water in the rinse tank, after which heaters 22 evaporate water from the emulsion and dry the oil of the emulsion which remains as an adherent coating on the strip.

As has been stated above, I believe that the foregoing treatment not only reduces any oxides which may be on the surface of the brightened electro-tinplate but also makes the surface layers of the tin passive or protects them to such an extent that they do not become oxidized to a material extent either before or during subjection to the oven temperatures at which lacquer or enamel is baked thereon. I believe that it is due to this reduction and passivation of the surface layers of the tin and the protection afforded by the non-oxidizing atmosphere and the final coating that the strong, tenacious adherence of I enamel and lacquer to tinplate treated by this method is largely, if not entirely, traceable.

This application is a continuation-in-part of my copending application Ser. No. 520,783 filed February 2, 1944, now abandoned.

Having thus described my invention so that others skilled in the art may be able to understand and practice the same, I state that what I desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The method of treating elongated brightened electro-tinplate which comprises the steps of making the tinplate a cathode, moving such tinplate endwise and successively deoxidizing tin surfaces thereof electrolytically in an aqueous, hexavalent chromium electrolyte, covering the thus deoxidized surfaces with a steam atmosphere while passing the tinplate from the electrolyte into and out of a body of washing liquid and thereby protecting said surfaces by said atmosphere against oxidation and substantially completely drying them after they pass out of the washing liquid, heating said surfaces for less than about one second to remove final moisture therefrom and forming an oil coating on said surfaces.

2. The method of treating elongated brightened electro-tinplate which comprises the steps of making the tinplate a cathode, moving such tinplate endwise and successively deoxidizing tin surfaces thereof electrolytically in an aqueous,

hexavalent chromium electrolyte, covering the thus deoxidized surfaces with a steam atmosphere while passing the tinplate from the electrolyte into and out of a body of washing liquid and thereby protecting said surfaces by said atmosphere against oxidation and substantially completely drying them after they pass out of the washing liquid, heating said surfaces for less than about one secondto remove final moisture therefrom, forming an oil coating on said surface, rinsing said coating in water and drying the coating.

3. The method of treating elongated brightened electro-tinplate which comprises the steps of making the tinplate a cathode, moving such tinplate endwise and successively deoxidizing tin surfaces thereof electrolytically in an aqueous, hexavalent chromium electrolyte, covering the thus deoxidized surfaces with a steam atmosphere while passing the tinplate from the electrolyte into and out of a body of washing liquid and thereby protecting said surfaces by said atmosphere against oxidation and substantially completely drying them after they pass out of the washing liquid, heating said surfaces for less than about one second to remove final moisture therefrom, forming an oil coating on said surfaces and drying the coating.

4. The method of treating brightened electrotinplate which comprises the steps of removing oxides from surfaces of such tinplate by making the tinplate the cathode in an aqueous electrolyte containing dissolved hexavalent chromium ions equivalent to those in from .5% to 75% by weight of alkali chromate and passing an electric current of from about 4 amps. to about 25 amps. per sq. ft. thru said electrolyte and tinplate for between about one second and about ten seconds,

removing electrolyte from the tin surfaces by passing the tinplate in a steam atmosphere into and out of a body of water, removing water from said surfaces by directing jets of steam under pressure at an acute angle thereagainst, drying the tin surfaces by heating them for less than one second and immediately protecting the tin surfaces against contact with air by covering them with an adherent oil emulsion film and removing moisture from said film.

5. The method of treating elongated brightened electro-tinplate, which comprises the steps of moving said tinplate endwise at a lineal speed of from about to about 800 feet per minute and successively treating increments thereof as follows: removing oxides from surfaces of such tinplate by making it the cathode in an aqueous electrolyte containing dissolved hexavalent chromium ions equivalent to those in from .5% to .75% by weight of alkali chromate and maintained at a temperature of between about F. and about 200 F. and passing an electric current of from about 4 amps, to about 25 amps. per sq. ft. thru said electrolyte and tinplate for between about one second and about ten seconds, removing electrolyte from the tin surfaces by passing the tinplate in a steam atmosphere into and out of a body of water at a temperature of about 180 F., removing water from said tin surfaces by directing jets of steam under pressure at an acute angle thereagainst, drying the tin surfaces by heating them for less than one second, covering the tin surfaces with an oil emulsion film, rinsing in water and heating said film.

ALVIN FREDERICK PRUST.

REFERENCES CITED The following references are of record in the 1c of this patent:

UNITED STATES PATENTS- Number Name Date 1,827,204 Mason Oct. 13, 1931 1,872,614 Wirshing Aug. 16, 1932 2,125,387 Mason Aug. 2, 1938 2,142,486 Antisell Jan. 3, 1939 2,203,062 Schueller June 4, 1940 2,215,143 Clayton Sept. 17, 1940 2,215,165 Sumner Sept. 17, 1940 2,234,593 Ferm et a1 Mar. 11, 1941 2,255,859 Quigley Sept. 16, 1941 2,266,330 Nachtman Dec. 16, 1941 2,274,963 Hopper Mar. 3, 1942 2,306,143 Stevenson Dec. 22, 1942 2,314,818 Cook et a1 Mar. 23, 1943 2,317,242 Allen et a1 Apr. 20, 1943 2,327,127 Rath Aug. 17, 1943 2,327,885 Grace et al Aug. 24, 1943 2,424,718 Stevenson July 29, 1947 FOREIGN PATENTS Number Country Date 479,746 Great Britain Feb. 7, 1938 

1. THE METHOD OF TREATING ELONGATED BRIGHTENED ELECTRO-TINPLATE WHICH COMPRISES THE STEPS OF MAKING THE TINPLATE A CATHODE, MOVING SUCH TINPLATE ENDWISE AND SUCCESSIVELY DEOXIDIZING TIN SURFACES THEREOF ELECTROLYTICALLY IN AN AQUEOUS, HEXAVANENT CHROMIUM ELECTROLYTE, COVERING THE THUS DEOXIDIZED SURFACES WITH A STEAM ATMOSPHERE WHILE PASSING THE TINPLATE FROM THE ELECTROLYTE INTO AND OUT OF A BODY OF WASHING LIQUID AND THEREBY PROTECTING SAID SURFACE BY SAID ATMOSPHERE AGAINST OXIDATION AND SUBSTANTIALLY COMPLETELY DRYING THEM AFTER THEY PASS OUT OF THE WASHING LIQUID, HEATING SAID SURFACES FOR LESS THAN ABOUT ONE SECOND TO REMOVE FINAL MOISTURE THEREFROM AND FORMING AN OIL COATING ON SAID SURFACES. 